package org.apache.lucene.search;

/**
 * Copyright 2004 The Apache Software Foundation
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.io.IOException;

import org.apache.lucene.index.Term;
import org.apache.lucene.index.TermEnum;
import org.apache.lucene.index.IndexReader;
import org.apache.lucene.util.ToStringUtils;

/** A Query that matches documents containing terms with a specified prefix. A PrefixQuery
 * is built by QueryParser for input like <code>app*</code>. */
public class PrefixQuery extends Query {
    private Term prefix;

    /** Constructs a query for terms starting with <code>prefix</code>. */
    public PrefixQuery(Term prefix) {
        this.prefix = prefix;
    }

    /** Returns the prefix of this query. */
    public Term getPrefix() {
        return prefix;
    }

    public Query rewrite(IndexReader reader) throws IOException {
        BooleanQuery query = new BooleanQuery(true);
        TermEnum enumerator = reader.terms(prefix);
        try {
            String prefixText = prefix.text();
            String prefixField = prefix.field();
            do {
                Term term = enumerator.term();
                if (term != null && term.text().startsWith(prefixText) && term.field() == prefixField) {
                    TermQuery tq = new TermQuery(term); // found a match
                    tq.setBoost(getBoost()); // set the boost
                    query.add(tq, BooleanClause.Occur.SHOULD); // add to query
                    //System.out.println("added " + term);
                } else {
                    break;
                }
            } while (enumerator.next());
        } finally {
            enumerator.close();
        }
        return query;
    }

    /** Prints a user-readable version of this query. */
    public String toString(String field) {
        StringBuffer buffer = new StringBuffer();
        if (!prefix.field().equals(field)) {
            buffer.append(prefix.field());
            buffer.append(":");
        }
        buffer.append(prefix.text());
        buffer.append('*');
        buffer.append(ToStringUtils.boost(getBoost()));
        return buffer.toString();
    }

    /** Returns true iff <code>o</code> is equal to this. */
    public boolean equals(Object o) {
        if (!(o instanceof PrefixQuery))
            return false;
        PrefixQuery other = (PrefixQuery) o;
        return (this.getBoost() == other.getBoost()) && this.prefix.equals(other.prefix);
    }

    /** Returns a hash code value for this object.*/
    public int hashCode() {
        return Float.floatToIntBits(getBoost()) ^ prefix.hashCode() ^ 0x6634D93C;
    }
}
